Quantitative depth profile analysis of high-Tc-superconductors with sputtered neutral mass spectrometry (SNMS)

Summary SNMS, a new surface sensitive as well as a bulk analysis technique, has been applied to the quantitative compositional depth profiling analysis of conductive and insulating thin films. Its performance is demonstrated by investigation of YBCO superconductor bulk analysis and sputter deposited layers on single crystalline substrates of SrTiO₃ and Al₂O₃. A stable stoichiometric volume has been observed in bulk material and thin films respectively. Inside a range of 500 nm from the surface, the composition deviates strongly from the stoichiometric concentration of Y and Ba. Comparative measurements with a freshly cleaved piece of YBCO bulk material which was immediately loaded into the ultrahigh vacuum analysis chamber show constant and stoichiometric concentration of all faced elements (Y, Ba, Cu, O) from the beginning of surface etching. The ratio of Y to Ba and Cu varied by less than 2%, the ratio Cu to oxygen by less than 5% from the nominal composition 1-2-3 (4).

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Quantitative Tiefenprofilanalyse von HT_c-Supraleitern mit SNMS

     

Quantitative depth profiling of argon in tungsten films by secondary ion mass spectrometry.

Depth profiling of Ar in Ar-implanted tungsten (W) films with an excellent detection limit was investigated by secondary ion mass spectrometry (SIMS). Depth profiles of Ar with the detection of Ar+ and ArCs+ secondary ions, which were produced by O2+ and Cs+ primary ions, respectively, were compared in view of the detection limit and the depth resolution. The detection limit of Ar monitoring Ar+ was limited by the carbon- and oxygen-containing molecular ion (C2O+) in the sample as well as in the SIMS instrument. It was observed that some of the Ar+ ions were produced in the vacuum above the sample surfaces, whereas the ionization of almost all C2O+ occurred at the samples. By using different energy spectra between Ar+ and C2O+, we showed that the energy-filtering technique is advantageous for suppressing C2O+ ion detection. It is also confirmed that the ArCs+ secondary ion is only slighting by the C2OCs+ mass-interference ion. A detection limit of 4 x 10(18) cm(-3) for monitoring Ar+ and 3 x 10(16) cm(-3) for monitoring ArCs+ was achieved under a primary-ion current density of 0.16 mA/cm2. The detection of ArCs+ ion rather than Ar+ was found to be superior in the detection limit and the depth resolution. We conclude that SIMS is useful for the determination of the Ar depth distribution in W films.     

Cold-Cathode ion source for sputtered neutral mass spectrometry of metals

A method involving cathodic sputtering and post-ionization in the electronflux of a Penning discharge is described for the analysis of metals.     

X-ray diffraction measurements and depth profiling by secondary neutral mass spectrometry on epitaxially grown high-Tc superconducting thin films

YBa₂Cu₃O_7– thin films were deposited by pulsed laser deposition (PLD) on various substrates with different misfit. X-ray diffraction (XRD) measurements were performed in order to characterize the growth quality of the films and to study the orientation between the films and the substrates. On the used substrates all investigated films are relaxed independently, and epitaxially grown who show a long range ordered two domain structure. The elemental concentration depth profiles of these films detected by secondary neutral mass spectrometry (SNMS) show homogeneous stoichiometric element distributions with slight deviation of the Y content.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Quantitative secondary ion mass spectrometry depth profiling of surface layers of cubic silver halide microcrystals

The present article describes depth-profiling studies on populations of cubic silver halide microcrystals (typical size between 400 and 600 nm). These crystals consist of mixed halides (Cl, Br, I) and are characterized by internal halide distributions such as core-shell structures. Determination of the spatial distribution of the different halides in the microcrystals offers valuable information for the optimization of the crystal design of new photographic materials. The first part describes the calibration of the sputtered depth, which is more complicated than in the one-dimensional case of flat surfaces. In a second part, three different quantification methods [halide intensity ratios, XCs₂⁺ detection (X=halide) and the infinite velocity method] are used to determine the mean composition of the surface layer as a function of sputtered depth in the silver halide crystals. Although particles of submicrometer size are obviously not the ideal samples for depth profiling, a good correlation with values obtained by scanning electron microscopy energy dispersive X-ray microanalysis and wavelength dispersive X-ray fluorescence bulk analysis could be achieved.     

Glycoprotein profiling by electrospray mass spectrometry

This work compares several different methods of site-specific analysis of glycoproteins using electrospray mass spectrometry. The glycoprotein, oLHalpha (ovine luteinizing hormone, alpha-subunit) was chosen as an appropriate example protein for these studies because of its biological relevance and extreme microheterogeneity. More than 20 unique glycoforms were detected for this glycoprotein at the Asn(56) site of oLHalpha. The carbohydrates present at this site affect receptor binding affinity, so understanding the great variety in the composition of these carbohydrates is important in studying ligand binding interactions. MS data was acquired on a quadrupole ion trap, a triple quadrupole, and a quadrupole time of flight mass spectrometer, and carbohydrate composition at the Asn(56) site of oLHalpha was determined using these instruments. Additionally, neutral loss and precursor ion scanning modes were also used to identify the glycoforms present, and these techniques were compared to the standard MS data. Of the three instruments compared in the study, the qTOF mass spectrometer achieved the lowest sample consumption, but all three instruments were useful in profiling the glycopeptide composition.     

Selective detection of polyaromatic hydrocarbons on diesel exhaust particles using sputtered neutral mass spectrometry

Aiming for the highly sensitive analysis of aromatic hydrocarbons in organic mixtures, selective ionization using an ultraviolet laser ionization technique was examined for the determination of sputtered neutral species on organic surfaces. The mass spectrum of a model mixture containing pyrene and n‐alkane showed that only pyrene was ionized and detected, whereas a mass spectrum without laser irradiation, i.e. in the case of secondary ion mass spectrometry, was dominated by many n‐alkane fragment peaks. This technique was applied for the detection of polyaromatic hydrocarbons adsorbed on diesel exhaust particles. Two kinds of polyaromatic hydrocarbons were clearly detected because many aliphatic fragment signals were suppressed by means of ultraviolet laser ionization. Copyright © 2013 John Wiley & Sons, Ltd.     

Chemically alternating langmuir-blodgett thin films as a model for molecular depth profiling by mass spectrometry

Langmuir-Blodgett multilayers of alternating barium arachidate and barium dimyristoyl phosphatidate are characterized by secondary ion mass spectrometry employing a 40 keV buckminsterfullerene (C60) ion source. These films exhibit well-defined structures with minimal chemical mixing between layers, making them an intriguing platform to study fundamental issues associated with molecular depth profiling. The experiments were performed using three different substrates of 306 nm, 177 nm, and 90 nm in thickness, each containing six subunits with alternating chemistry. The molecular subunits are successfully resolved for the 306 nm and 177 nm films by cluster ion depth profiling at cryogenic temperatures. In the depth profile, very little degradation was found for the molecular ion signal of the underneath layers compared with that of the top layer, indicating that the formation of chemical damage is removed as rapidly as it is formed. The resolving power decreases as the thickness of the alternating subunits decrease, allowing a depth resolution of 20 to 25 nm to be achieved. The results show the potential of LB films as an experimental model system for studying fundamental features of molecular depth profiling.     

Comparative analysis of layered materials using laser-induced plasma spectrometry and laser-ionization time-of-flight mass spectrometry

Laser-induced plasma spectrometry (LIPS) and laser ionization time-of-flight mass spectrometry (LI-TOFMS) have been evaluated for the in-depth analysis of layered materials. LI-TOFMS shares with LIPS important advantages in terms of speed of analysis and negligible sample handling. However, additional features such as real multielemental capabilities and the absence of background contribution must be added to the former. In order to have a useful estimation of the potential of each technique, an in-depth characterized Zn-coated steel has been analyzed. Without complete optimization of the system, the averaged ablation rate has been measured to be in the range 20–30 nm/pulse without beam conditioning or optical modifications.     

Calibration of depth profiles of microparticles measured with plasma-based secondary neutral mass spectrometry

A gravimetric method is presented for the easy determination of sputter erosion rates for powders, applicable also to non-conducting materials. Measurements of the erosion rates of 22 powders gave an average value of 0.4 nm/s ±50% for bombardment with 400 eV Ar⁺ at 1 mA/cm². The validity of the data has been demonstrated with technical pigments and outdoor aerosol particles.     

Investigation of the profiling depth in matrix-assisted laser desorption/ionization imaging mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry is generally considered to be a surface analysis technique. In this report, the profiling depth of imaging mass spectrometry was examined. MALDI matrix solution was found to be able to gain access to the tissue interior and extract analyte molecules to the tissue surface. As a consequence, prazosin, a small molecule pharmaceutical compound, located as deep as 40 microm away from the surface was readily detected after matrix application. Likewise, cytochrome c, a 12 kDa protein, was also detectable from the tissue interior. Moreover, for prazosin, not only the extent of matrix effect, but also the extraction efficiency of the matrix solvent appeared to be dependent on the type of tissue. These results indicated that experimental conditions that decrease the matrix solvent evaporation during matrix application may increase analyte extraction efficiency and hence sensitivity of the analysis. Furthermore, thin sections should be used to avoid differential extraction efficiency of matrix solvent in different tissues for whole-body analysis.     

表达蛋白质质谱分析

对基因编码的蛋白质进行系统分析可以为注释基因组信息和研究疾病发生机理提供参考.质谱因其高通量、高灵敏度和高精度等特点成为蛋白质表达谱研究的核心技术.过去10年,质谱技术的发展大大促进了蛋白质表达谱的研究.本文综述了蛋白质表达谱的定性和定量研究进展,并展望了进一步的研究方向.     

Quantitative profiling of phosphatidylethanol molecular species in human blood by liquid chromatography high resolution mass spectrometry

Phosphatidylethanol (PEth) is a group of aberrant phospholipids formed in cell membranes in the presence of ethanol by the catalytic action of the enzyme phospholipase D on phosphatidylcholine. Recently published literature has demonstrated the existence of several molecular species of PEth in samples drawn from alcohol-dependent subjects. A novel liquid chromatography high-resolution mass spectrometry (LC-HRMS) method coupled with a lipidomic strategy was developed and validated for the quantitative profiling of PEth molecular species in human blood collected from heavy and social drinkers. Chromatography was performed on a C18 column using acetonitrile, 10mM ammonium acetate, and 2-propanol as mobile phases with a 22-min gradient. HRMS experiments were performed on an LTQ-Orbitrap XL hybrid mass spectrometer equipped with an electrospray ionization source operated in negative ion mode. The theoretical masses of [M-H](-) of PEth species were calculated from the elemental chemical formula by varying the length and unsaturation grade of the fatty acid side chains; identification of PEth species in blood was achieved by searching the accurate masses of the targeted compounds in the acquired full-scan LC-HRMS chromatogram. The chemical structure of tentatively identified PEth species was elucidated through HR multiple mass experiments. The validated LC-HRMS method was selective, as warranted by HRMS at 60,000 resolution and 4 ppm accuracy. Linearity was observed in the 0.001-2.000 μM range, and limit of detection of 0.0005 μM and limit of quantitation of 0.001 μM were obtained for single PEth species. Imprecision and inaccuracy were always lower than 10% and 15%, respectively. The identification capabilities of the method were tested on blood samples collected from heavy drinkers (n=11), social drinkers (n=8), and teetotalers (n=10). The high sensitivity of the method led to the simultaneous identification of 17 different PEth molecular species in blood collected from heavy drinkers, and 2 PEth species (16:0/18:1 and 16:0/18:2) in blood collected from social drinkers.     

Atomic/molecular depth profiling of nanometric‐metallized polymer thin films by secondary ion mass spectrometry

The capability of secondary ion mass spectrometry (SIMS) to perform atomic and molecular in‐depth analysis in complex nanometric‐metallized thin polymer films used to manufacture capacitors is demonstrated through three different case studies related to failure analysis. The excellent repeatability and sensitivity of the technique allow us to study the degradation process of the nanometric‐metallized layer in the capacitor films and the accurate location of the metal‐polymer interface. The analysis of the sample is challenging due to the extreme difference in conductivity between layers, and the reduced thickness of the metallization grown on top of a rough polymeric base. However, SIMS has provided reliable and reproducible results with relative standard deviation (RSD) values better than 1.5% in the metallic layer thickness estimation. The detailed information of atomic and molecular ion in‐depth distributions provided by SIMS depth profiling has allowed the identification of different factors (demetallization, generation of interstitial oxide regions, and diffusion processes or modification in the metallization thickness) that can be directly related to the origin of the lack of performance of the mounted devices. Copyright © 2010 John Wiley & Sons, Ltd.     

Quantitative profiling method for phytohormones and betaines in algae by liquid chromatography electrospray ionization tandem mass spectrometry

A liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed for the quantitative determination of phytohormones and betaines in algae. The results showed that phytohormones and betaines were separated with high efficiency on Hypersil Gold C₁₈ and Cnwsil SCX columns. Mass spectrometric detection was performed using positive or negative electrospray ionization in selective reaction monitoring mode (SRM). Linearity of the method was good with correlation coefficients (r²) > 0.9951 in the range of 0.005–5 mg/L. The limits of detection were from 0.004 to 0.86 µg/L and the limits of quantification were in the range from 0.01 to 2.8 µg/L for the investigated phytohormones and betaines. The obtained recoveries varied between 61.33 and 90.39%, and the relative standard deviations were <15%. Using the developed methods, seven types of phytohormones and two types of betaines in Laminaria japonica, and seven types of phytohormones and one type of betaine in Pyropia haitanensis, which were collected in Xiangshan, Zhejiang Province, China, were determined. Thus, LC‐MS/MS was demonstrated to be a powerful tool for the comprehensive analysis of phytohormones and betaines in algae, owing to its large dynamic range and excellent sensitivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Carbon-13 labeling for improved tracer depth profiling of organic materials using secondary ion mass spectrometry

13C labeling is introduced as an alternative to deuterium labeling for analysis of organic materials using secondary ion mass spectrometry (SIMS). A model macromolecular system composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) was used to compare the effects of isotopic labeling using both deuterium substitution (dPS) and 13C labeling (13C-PS). Clear evidence is shown that deuterium labeling does introduce changes in the thermodynamic properties of the system, with the observation of segregation of dPS to an hPS:dPS/hPMMA interface. This type of behavior could significantly impact many types of investigations due to the potential for improper interpretation of experimental results as a consequence of labeling-induced artifacts. 13C labeling is shown to provide a true tracer for analysis using SIMS.